Still need help on 93 SC. won't stay running


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Hi All, I'm back again looking for help with 93 SC. Long story. Last year I installed a new engine and it's never run since. Crusty wires on main engine harness
#1 I replaced it with NOS/OEM engine harness. Ran for 10 seconds at High RPM and shuts off.
#2 Then it lost spark. Replaced harmonic balancer & new Crankshaft sensor bought from Bill @ SCP. Fired up ran like crap and died and lost spark again.
#3 Replaced DIS module & camshaft sensor with new ones. It recovered spark. Fired up High RPM and dies.
#4 I still do have spark. Plugged all vacuum ports except fuel regulator & blower flapper. Same thing fires high rpm and dies. I can keep it running if I modulate throttle. Car will not idle.
#5 It did throw a check engine light. (my obd1 tester crapped out, I bought another one)
#6 Got the new obd1 tester today and here are the codes: 113, 118, 123, 126, 341, 565. I see what the codes mean in the book (but I'm not that great at trouble shooting) and I'm at a loss??
Do I Buy a TPS & IAC & MAF..... they all are 1993 vintage age and the only thing left I think. Any advice will help..
I could have put in a 351 Winsor with a carb, for all the time and money I got tied up in this SC.
But I do like the sound of the supercharger.
I rarely replaced sensors on EEC Ford systems, in my previous diagnostic days. Except for a crank sensor, on occasion. The codes 113,118,123, and 126 indicate the signal return, ( or a sensor ground ), is missing. This would cause a ref signal high condition. I would look close at connector C166, , by the EEC diag connector, back in the right rear corner of the engine compartment. Check both of those engine harness connectors. Also, look at the black one wire connector, coming from the battery ground terminal pigtail. The othe end goes to the core support.
After that, check that you don't have water dripping down on your PCM, behind the right kick panel. Also, back probe the black/white stripe wire, at any of the listed sensors,(IAT,ECT,TPS,MAP0. Anyone, that is easy to get to. Key on, engine off. Should be .3 VDC, or less. If higher, like 1-4.8 VDC, that's your problem. Clear codes, recheck after repairs. A good OBD1 scanner should let you see data, by that year.
C166 doesn't show up on the SC component page of the EVTM? There is no water dripping near PCM and I know the black one wire connector has good ground to core support but I'll recheck it and probe all the other grounds. If any of the sensors read more than .3 VDC what would be the fix for that?
C166 doesn't show up on the SC component page of the EVTM?

The EVTM for my '90 SC says this it is "right front of firewall on relay bracket" (as noted above) - I'm guessing, if you don't see it in your '93 EVTM, this is where earlier systems used total of 3 relays there, and we hear only 2 relays are found on some cars/later models.
I'm talking about the two engine harness connectors, right by where the passenger hood strut is attached. One of those connectors has the sensor wiring. I think you said you replaced the engine harnesses.


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Ah yes...THOSE connectors...

C166 is the lower one. I know for sure since at one time, I found less than 0.5v supply at the sensors it feeds...when I did a drop test across that connector, I found 0.5v going in but 0.3v coming out. No wonder the ECU seemed to be acting on bad advice.

Opened the connector, found green corroded connections where it mated. Cleaned things up, reassembled and all was good. I now make it a practice of checking that connector. and several others, on a biennial basis, or as required. Oregon weather does an SC no favors, after all.



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Yes I did replace the harness from the ECU that goes thru the fire wall and rebuilt the short ignition harness (dis, cmp, ckp, coil), but have done nothing with the other TPS, IAC...….harness. I'll look again at both connectors to engine harnesses for any corrosion, also I'll check the sensor connectors later today if it warms up. This car has sat inside my shed (shed has roof & sidewalls but no end walls) with the hood off since the engine replace (tried to keep engine bay covered but sometimes it was not) so yes moisture is playing a part.
I'm sure the on-again/off-again spark was the DIS as it had some hairline cracks.
I Just went out to the shed quickly this morning to wiggle and unplug and re-plug connectors, no green but some could stand to be cleaned. Tried to start, it fired up (no high RPM this time but just sputtered and dyed. Tried again with modulating gas pedal sputtered longer then died)
Going to run to town and get some wire connector spray cleaner and try again this afternoon when it gets to 45deg. or tomorrow when it gets to 63deg. I'll keep U posted
I wouldn't waste time and money, on "cleaner", and parts, until there is some measurements taken with your volt meter. The ECT, (coolant sensor), should have around 2-2.5 volts cold on the light green/yellow wire. You Also clear all codes, and redo a KOEO test, and see what you get. Also, on those connectors, just spray them with WD-40, and plug them in, and out a couple of times.
Ok, I did clean connectors, and tried to start, it still will not idle but no high rpm. I then saw your comment about testing DCV on the coolant sensor. Colors are green/red and brown/red. I Did pin test KOEO for both to ground, green/red 4.18 volts and brown/red 4.5 volts.
Other sensor with single yellow wire has 10.9 volts.
OK also I have no coolant in motor yet, just trying to dry fire before it's buttoned up, if that makes a diff? motor has never run for more than 5sec.

Also How do I clear all codes


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The brown/red wire is actually gray/red. The gray/red wires measure like a ground, and comes from pin 46 on the ECM connector. That is your problem. The EEC sensors are not being pulled down low. There is one more EEC engine connector, on the right side of the engine, down by the starter, and knock sensor. Trace from knock sensor, and right side oxygen sensor. There are 3 engine to EEC connectors. Also, the signal yellow wire is connected to a cold engine lock-out switch, for the Auto climate control. Your gray/red wires, are black/white on my diagram, for a older supercoupe than yours. Sorry for my mix up.


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Yes the GY/R have been my suspect wires. I'm fairly sure I have the 3 engine to EEC connectors hooked up to the new wire harness, But I'll recheck them.
Question: what is the purpose of the GY/R wire @ C228 to the P/Y wire and GY/Y wire coming thru the neutral switch from R/LB wire from PCM pin 30? That's a mouth full. This car is an Automatic.
Reason I ask: is I had wire problems in the beginning with the starting system going thru that switch out thru an after market anti-theft/auto start/auto lock system that was on the car. I cut it out at the W/PK and ran new wire to the R/LB at the starter relay. NOT SURE if I may have disabled that P/Y 480 wire?


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Ok got all codes cleared out, Checked all sensor connector plugs..aok. I did a KOEO test at the ECT (coolant sensor) GY/R wire reads 5.3 volts & LG/R was 4.3 volts, I then unplugged sensor wiring harness at connector C172 did KOEO test and got same 5.3 volts on GY/R & then unplugged C173 and got same 4.3 volts on LG/R. Tried to start and got same thing sputter & die, modulate throttle long enough to get check engine light. Ran codes and got all the same ones as before.
I Still need to trace the GY/R wire going to the neutral switch up to PCM pin #30. Think that could be it???
I'm Still at a Lose
"The brown/red wire is actually gray/red. The gray/red wires measure like a ground, and comes from pin 46 on the ECM connector. That is your problem. The EEC sensors are not being pulled down low."

The gray/red wire gets it ground, (near 0 voltage), from, and only from pin 46 at the PCM, (engine computer).
So if I have reading 5.3 volts at the unplugged C172 GY/R coming from PCM pin 46. Where do I look next?
Where do I look next?

As SC-AL suggested above, I'd begin checking for 5.x V at the TPS, crank, cam and ECT sensors, repeating for any you've already checked. Note that the connectors need to be in place while testing, or the ECU won't send volts across the related wire(s). You need to be able to backprobe the connector at each sender, with the key on. I'm most interested in the signal volts being fed to the TPS (sorry if I missed it ), also while back probing the TPS, try to check it's output with key on and throttle body moved thru a full swing - If any fail (<5.xv), I might be looking for another ECU, at least a known good one to test with.
Thanks so mush Guys!! I get frustrated trouble shooting electrical ( brain turns to mush)
I'm going to get at it again tomorrow. and report in what I find.
So I'm looking for 5.x V at the TPS, crank, cam and ECT sensors and if less than <5.xV the ECU may be toast? (I have a 90 automatic ECU, Will that work on my 93 automatic if needed?) And I'll test TPS thru full swing.
Also I'm rechecking all GY/R wires to be as close to 0 volts.
...if less than <5.xV the ECU may be toast?'s just that if you find <5.xV at those sensors across the board, I'd favor stopping at this point and doing an ECU swap to, again, eliminate it as suspect.
(I have a 90 automatic ECU, Will that work on my 93 automatic if needed?

Dunno - only if they have matching #'s, I guess.

And about testing the're looking for a smooth swing up to approx. 4.70V DC, and back to zero...if it jumps around or hangs or does nothing, time to replace .
Well lets start with all tests were Voltage Drop Testing done KOEO and everything was plugged in.
* All GY/R's wires tested 5.38 ish volts. And I did test the GR/R wire going to the ECU, with the new harness C161 Unplugged (KOEO) same 5.38v
* ECT thru volts 0.78, LR/R wire 4.5v
* IAT thru volts 0.73, Y/W wire 4.5v
* IAC thru volts 0.12 and each wire along was11.5v
* BARO GY/R to DB/LG = 0.5v, GY/R to BR/W = 0.7v, thru DB/LG to BR/W = 0.2v
* Octane Adjust Plug thru 0.5, one wire has 0.95v and other has 0.45v
* Knock Sensor thru 2.3v
* TPS thru volts BR/W to GY/W swing 0.63v closed to 0.08v WOT and BR/W = 4.61v no swing and GR/W 5.24v closed & 4.69v WOT
Didn't test crank, cam sensors or HO2S R&L since they're new.
The ECU area all looked dry last month when harness was replaced, but I'll probably be back there.
What steps you all think are next?